In traditional hydrocarbon processes for preparing alkenes the alkane(s) is/are dehydrogenated to one or more alkenes with concomitant formation of hydrogen. There are several problems associated with these processes. For example, due to the chemical equilibrium between the alkane(s), alkene(s) and hydrogen it is in general not possible to convert the alkane(s) completely into the desired alkene(s). The selectivity to the desired alkene(s) may be low because cracked products and coke may be formed at the expense of starting material and/or reaction product, in particular in the dehydrogenation of unbranched alkanes.
According to the disclosures in, inter alia, U.S. Pat. Nos. 2,570,067, 2,638,455, 2,576,034 and 3,711,569, it is preferred to employ in the vanadia catalyzed dehydrogenation reactions catalysts which have a relatively high vanadia content, for example above 15% w, calculated as divanadium pentoxide, relative to the weight of the catalyst. In other documents, inter alia in U.S. Pat. Nos. 2,814,650, 3,228,992, U.S. Pat. No. 4,607,129 and 4,644,089, a preference for catalyst with a lower vanadia content is expressed. Likewise, the temperature at which the dehydrogenation reactions can be carried out may vary between wide limits, for example, from 400.degree. C. to 700.degree. C.
U.S. Pat. No. 4,607,129 discloses a process for the preparation of alkenes. A feed containing one or more C.sub.2 -C.sub.10 alkanes is contacted at an elevated temperature with a catalyst containing 1-15% w vanadia, calculated as divanadium pentoxide relative to the weight of the catalyst, on a refractory support. In the process the most preferred temperature range for contacting the feed with the catalyst amounts to from 482.degree. to 593.degree. C. and the most preferred range of reaction times amounts to from 4 to 8 seconds. In the processes referred to, the yield of the desired alkene(s) leaves room for improvement. Therefore, it would be advantageous to provide a dehydrogenation process with an improved yield of alkenes.